Elastomeric engine mounts have long been incorporated in motor vehicles to isolate engine vibrations from the chassis and vehicle body. The isolation of vibration provides a more comfortable ride. In its most common and basic form, an engine mount has one horizontal plate secured to the frame of the motor vehicle with a block of rubber interposed between the two plates and bonded thereto. The rubber undergoes compression during vibrations of the engine.
Further developments have a plurality of separate rubber pads stacked in an assembly to isolate vibrations. One such construction is disclosed in U.S. Pat. No. 2,076,034 issued to Lampman on Apr. 6, 1937.
It is also known to use vibration isolating mounts where the rubber acts in shear by attaching one vertical plate to the supporting member and the second spaced vertical plate to the supporting member with the rubber interposed therebetween and bonded to the two vertical plates. One such construction is disclosed in U.S. Pat. No. 2,257,804 issued to Lord on Oct. 7, 1941. It is known that rubber acting in shear has a lower resilient rate than rubber acting in compression. Hence, shear mounts have the advantage of obtaining a lower resilient rate than comparable compression mounts.
It is also known to change the characteristics of the rubber by introducing cavities within the rubber which changes the vibration characteristics. The cavities effectively lower the resilient rate of the mount. One such construction is disclosed in U.S. Pat. No. 3,132,830 issued to Adloff on May 12, 1964.
Furthermore, it is disclosed in U.S. Pat. No. 2,925,973 issued to Aebersold on Feb. 23, 1960 to use tubular housings mounted to one of the engine or chassis with an elastomeric sleeve fitted therein having an eccentrically place aperture therethrough. A bolt extends therethrough to the aperture and is fixed to the other of the engine or chassis. The thick portion of the elastomeric sleeve is loaded and the thin portion is unloaded in compression.
U.S. Pat. No. 3,035,799 issued to Pierce discloses another compression mount where one elastomeric pad is compressed more than a second elastomeric pad.
British Pat. No. 890032 to Hirst discloses a resilient mount having two annular rings of elastomer. The outer ring is loaded in shear and the inner ring is unloaded in shear until an excess load is applied to the mount. However, this mount is deficient for use with motor vehicles because the mount does not use the elastomeric ring in damping vibrations in the upward direction. The mount has its inner sleeve merely lift off the frame and all the upward vibration is absorbed by the preloaded elastomeric ring.
It is desired to improve vibration isolation of an engine with respect to the chassis by use of a mount which is constructed such that some elastomeric material is preloaded in shear while other elastomeric material is effectively unloaded when the engine is statically mounted onto the chassis. It is also desired to have a mount where all the elastomeric material undergoes shear for both upwardly and downwardly directed vibrations.